1. Field of the Invention
The present invention relates to inverting a folded sheet that comprises a large panel and a small panel that is folded, at a first edge side of the sheet, against the large panel on a first side of the sheet.
The terms “large panel” and “small panel” are to be understood as referring to the width of the respective panel in a lateral direction, i.e. transverse to the fold line(s) of the sheet. Thus, the small panel is narrower than the large panel. The fold lines define the extension of the panels. The sheet is, for example, a z-folded sheet having two parallel fold lines or, in particular, a sheet having an engineering fold, also known as a fold-out. An engineering fold is an asymmetric z-fold such as schematically shown in FIG. 5. The folded sheet has a large back panel and small center and front panels. In use, the front panel of the folded sheet may be pulled out to expand the sheet to its full width.
2. Background of the Invention
U.S. Pat. No. 5,207,412 describes a document integrator that allows stacking regular sheets as well as z-folded oversize sheets. A folded oversize sheet exits a sheet folder with its folded edge as the leading edge and is conveyed to a sheet inverter disk. The sheet is inserted into a slot of the sheet inverter disk, which then rotates to invert, i.e. flip over, the oversize folded sheet. The sheet is stripped from the inverter disk when the slot containing the folded oversize sheet passes through a stripping wall. The sheet is then conveyed by a vacuum transport belt towards a second sheet inverter disk that places the sheet on a stacker tray. Although the vacuum transport belt holds the inverted sheet thereon, a blower is provided for blowing a stream of air onto the inverted folded oversize sheet from above, so as to further prevent the sheet from unfolding.
The inventors have found that, when inverting a folded sheet using a conventional sheet inverter disk or similar device, the problem may arise that the folded sheet unfolds while rolling out from the sheet inverter disk, if the sheet is fed to the sheet inverter disk with its folded edge as the trailing edge and the small folded panel is the top panel before inverting.
In particular, it has been observed that, while the large panel is rotated and bent by the inverting element, the small panel may assume a straight form, such that the “inner edge” of the folded sheet, i.e. the edge of the small panel that is distant from the outer edges of the folded sheet, separates from the curved large panel. In other words, while the leading edge of the large panel follows the curved contour of the inverting element, because it is accommodated in a slot of the inverting element, the small panel may tangentially protrude from the large panel.
It may then happen that the “inner edge” gets ahead of the trailing edge of the sheet on top of a receiving member for receiving the sheet, such as a stacker tray, for example. Thus, during inverting the sheet, the sheet unfolds. The inventors have found that the described problem is particularly pronounced in the described case of a z-folded sheet comprising a large panel and a small, folded panel, which is to be fed to the inverting device with its folded edge as a trailing edge such that, after inverting the sheet, the folded, small panel is to be positioned below the large panel. However, a similar problem may arise with different sheet configurations and/or orientations.